3GPP (The 3rd Generation Partnership Project), 3GPP2 (The 3rd Generation Partnership Project 2), and WiMAX (Worldwide Interoperability for Microwave Access) are known as examples of a mobile communication system in which a mobility anchor provides mobility to a terminal. The mobility is implemented by a protocol such as GTP (GPRS (General Packet Radio Service) Tunneling Protocol), MIPv6 (Mobility IPv6), PMIPv6 (Proxy MIPv6), MIPv4 (Mobility IPv4), PMIPv4 (Proxy MIPv4), or the like. GTP, MIPv6, and PMIPv6 are adopted as protocols for implementing mobility (mobility protocols) in 3GPP, whereas MIPv4, MIPv6, PMIPv4, and PMIPv6 are adopted in WiMAX. Any of the mobile communication systems and any of the mobility protocols have commonality in their basic operation of transferring traffic addressed to a mobile terminal to a point of connection to this mobile terminal.
In such mobile communication systems, a system is proposed in which a proxy delivery server is disposed between a core network and an external network in order to suppress a delay of traffic and to maintain the continuity of a service a mobile terminal is using even if mobility anchor relocation takes place (see PTL 1). This system will be described briefly with reference to FIG. 1.
Referring to FIG. 1, a case will be considered where a plurality of proxy delivery servers 600a and 600b are disposed between an external network and a core network, and where gateway (GW) relocation from an access network GW 200a to another access network GW 200b and anchor relocation from a mobility anchor 100a to another mobility anchor 100b take place due to a move of a terminal 400. When a relocation request is made from the mobility anchor 100b, the proxy delivery server 600b makes a context request to the proxy delivery server 600a, which is relaying the delivery of a content to the terminal 400, and acquires context information related to the relaying of the content.
The context information includes, for example, content location information, session information, and the like. The content location information indicates a location in the content to be delivered up to which the content has been delivered to the mobile terminal 400, and is expressed by elapsed time, the number of bytes, the number of key frames in a compressed image stream, or the like from the head of the content. The session information is information required to allow a session with the mobile terminal 400 to continue. In case of the HTTP/TCP protocol, the session information includes, for example, HTTP header information that the transmission to the mobile terminal 400 is not completed, a source address, a destination address, TCP source and destination port numbers, a sequential number, an acknowledgement number, flag information to be set in the flag field of the TCP header, a window size, and transmission buffer information.
When receiving such context information, the proxy delivery server 600b uses this context information to reproduce the state of the session for delivery of the content between the proxy delivery server 600a and the terminal 400, and uses the reproduced session to forward the subsequent part of the content from a service providing server 500 to the terminal 400.
The provision of proxy delivery servers as described above makes it possible to reduce the delay time of traffic and to achieve efficient use of network resources even if there is a long distance in terms of topology between the mobility anchor 100a and the access network GW 200b. 